1. Field of the Invention
This invention relates generally to processing and manipulation of optical signals. More particularly, embodiments of the invention are concerned with systems and devices for performing processes such as dynamic tapping, splitting or attenuation of optical signals.
2. Background of the Invention
Increased demand for data communication and growth of the internet have resulted in increased demand for communication capability within metropolitan areas. There has also been an equally large increase in demand for communication capability between large metropolitan areas. Optical communication systems formed by networks of fiber optic cables are being developed and installed to meet this increased demand.
Various types of optical switches and techniques are currently used in communication systems and computer systems. Many currently available optical switches are based upon optoelectric and electrooptic conversion of light signals and electrical signals within the associated optical switch. One type of presently available optical switch includes a matrix of thermooptic switching elements interconnected by waveguides formed on a silica substrate. Switching of light signals is accomplished by the use of thin film heaters to vary the temperature of the switching elements. Electrical circuits are also provided to supply switching current to the heaters. A heat sink may be provided to dissipate heat caused by the switching operations. One example of such switches is shown in U.S. Pat. No. 5,653,008.
Some presently available optical switches include a semiconductor substrate with vertical current flow to heat active regions of an associated optical switch. One example of such switches is shown in U.S. Pat. No. 5,173,956. Some optical switches require mode perturbation to generate required mode patterns for the desired switching function. Examples of such optical switches include directional couplers and Mach Zhender interferometers. Such optical switch designs often have poor scalability, relatively high manufacturing costs and low optical signal bandwidth.
Various types of optical signal amplifiers, wavelength division demultiplexers, optical switches, wavelength division multiplexers and techniques are currently used in optical communication systems. Optical signal amplifiers, wavelength division multiplexers and demultiplexers and other components associated with optical communication systems typically function best when respective signal levels of associated optical signals are substantially equal with each other. A variation in signal level of multiple wavelength optical signals may result in an undesirable signal to noise ratio and resulting poor performance by switches, amplifiers and other optical components.
Multiple wavelength optical signals are often collectively amplified by a light amplifier. The amplification factor of many light amplifiers is dependent upon the wavelength of each optical signal. Therefore, amplification factors for multiple wavelength optical signals often vary depending on the specific wavelength of each signal. The resulting difference between signal levels of respective multiple wavelength optical signals amplified by a single amplifier is often relatively small. However, when a large number of light amplifiers (ten or more) are used in a fiber optic communication system, the variation in signal levels becomes cumulative and may result in unsatisfactory lowering of associated signal to noise ratios. Therefore, variable optical attenuators are often provided at the input stage and/or output stage of light amplifiers in both large metropolitan communication systems and long distance fiber optic communication systems to adjust signal levels of multiple wavelength light signals to maintain desired signal to noise ratios.
Variable optical attenuators are often included in optical communication systems to maintain a desired signal level for each optical signal or wavelength. Examples of variable optical attenuators (VOA) include natural density filters which are often used to suppress the amount of light depending on wavelength characteristics. Other variable optical attenuators include mechanical devices which position a glass substrate so that light signals may be attenuated by varying the position of the glass substrate. Still other variable optical attenuators attenuate light signals by rotating the polarization of each light signal as it passes through a Faraday element.
Optical taps are also included in many optical communication systems to monitor both performance of individual components and performance of the overall system.